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<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
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  <script>
    const age = 20; // 只读变量
    const AGE = 30;
    const MAX_AGE = 40;
    // const age; ×
    // age = 30; ×
    console.log(age);
  </script>
</body>

</html>